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strtok() and EOL

 
 
Fernando Barsoba
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      11-29-2005
Hi,

I'm using strtok() in the following way:

void obtain_param(char *pmsg, CONF_PARAMS *cnf ) {
char *s1, *s2;
size_t msg_len;

s1 = strtok (pmsg,":");
if (s1) {
s2 = strtok (0, "");
msg_len = strcspn(s2, "\n");
if (memcmp(s1, "message", sizeof("message")) == 0) {
cnf->msg_length = msg_len;
cnf->message = malloc(msg_len);
memcpy(cnf->message, s2, msg_len);
cnf->message[msg_len]='\0';

....

I extract the information from a configuration file. For some reason,
sometimes I get for msg_len 15 for this message:

>>message:this is a test


(when 'this is a test\n' is only 14 characters long, w/o the '\n')

In other installations (Linux) works just fine, but in my
Eclipse/CDT/cygwin sometimes is not.

Am I using strtok incorrectly? is the 's2' pointer messing things up?

Thanks,

F~
 
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Jack Klein
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      11-29-2005
On Tue, 29 Nov 2005 15:16:17 GMT, Fernando Barsoba
<(E-Mail Removed)> wrote in comp.lang.c:

> Hi,
>
> I'm using strtok() in the following way:
>
> void obtain_param(char *pmsg, CONF_PARAMS *cnf ) {
> char *s1, *s2;
> size_t msg_len;
>
> s1 = strtok (pmsg,":");
> if (s1) {
> s2 = strtok (0, "");
> msg_len = strcspn(s2, "\n");
> if (memcmp(s1, "message", sizeof("message")) == 0) {
> cnf->msg_length = msg_len;
> cnf->message = malloc(msg_len);
> memcpy(cnf->message, s2, msg_len);
> cnf->message[msg_len]='\0';
>
> ...
>
> I extract the information from a configuration file. For some reason,
> sometimes I get for msg_len 15 for this message:
>
> >>message:this is a test

>
> (when 'this is a test\n' is only 14 characters long, w/o the '\n')
>
> In other installations (Linux) works just fine, but in my
> Eclipse/CDT/cygwin sometimes is not.
>
> Am I using strtok incorrectly? is the 's2' pointer messing things up?
>
> Thanks,
>
> F~


Where did the text string passed in 'pmsg' come from? Was it read
from a file? If it was read from a file, was the file opened in text
or binary mode? If you are reading a text file opened in binary mode
under Windows, you are getting the string as it appears in the file,
which would be:

"message:this is a test\r\n"

--
Jack Klein
Home: http://JK-Technology.Com
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Mike Wahler
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      11-29-2005

"Fernando Barsoba" <(E-Mail Removed)> wrote in message
news:5h_if.6989$6e5.1530@trnddc09...
> Hi,
>
> I'm using strtok() in the following way:
>
> void obtain_param(char *pmsg, CONF_PARAMS *cnf ) {
> char *s1, *s2;
> size_t msg_len;
>
> s1 = strtok (pmsg,":");
> if (s1) {
> s2 = strtok (0, "");
> msg_len = strcspn(s2, "\n");
> if (memcmp(s1, "message", sizeof("message")) == 0) {
> cnf->msg_length = msg_len;
> cnf->message = malloc(msg_len);
> memcpy(cnf->message, s2, msg_len);
> cnf->message[msg_len]='\0';
>
> ...
>
> I extract the information from a configuration file. For some reason,
> sometimes I get for msg_len 15 for this message:
>
> >>message:this is a test

>
> (when 'this is a test\n' is only 14 characters long, w/o the '\n')
>
> In other installations (Linux) works just fine, but in my
> Eclipse/CDT/cygwin sometimes is not.
>
> Am I using strtok incorrectly? is the 's2' pointer messing things up?


Are you perhaps opening your file in binary mode? Note that
some OS's store newline as more than one character in text files.
E.g. Windows uses CR/LF pair and typical Windows C implementations
represent '\n' internally as LF (this would give the behavior
you describe if file were opened in binary mode on such systems
-- the 'extra' CR character would count as part of length returned
by 'strcspn()').

If you're not using it already, try text mode.

-Mike


 
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David Resnick
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Posts: n/a
 
      11-29-2005

Fernando Barsoba wrote:
> Hi,
>
> I'm using strtok() in the following way:


Probably fine, but you do know the issues with strtok, right?
In clc it is not re-entrant. In (OT) land, it is often not threadsafe
either. It is probably fine as you use it below.

>
> void obtain_param(char *pmsg, CONF_PARAMS *cnf ) {
> char *s1, *s2;
> size_t msg_len;
>
> s1 = strtok (pmsg,":");
> if (s1) {
> s2 = strtok (0, "");


I'm not totally sure the empty string is legit here, perhaps others
can say. Works fine if you say ":" too.

> msg_len = strcspn(s2, "\n");
> if (memcmp(s1, "message", sizeof("message")) == 0) {


Do you intend to compare the '\0' as you are? sizeof("message") is 8.
Fine either way, strtok will have put one in.

> cnf->msg_length = msg_len;
> cnf->message = malloc(msg_len);


You don't allocate enough space here for the string including the '\0'

> memcpy(cnf->message, s2, msg_len);
> cnf->message[msg_len]='\0';


One byte overwrite here.

>
> ...
>
> I extract the information from a configuration file. For some reason,
> sometimes I get for msg_len 15 for this message:
>
> >>message:this is a test

>
> (when 'this is a test\n' is only 14 characters long, w/o the '\n')
>
> In other installations (Linux) works just fine, but in my
> Eclipse/CDT/cygwin sometimes is not.
>
> Am I using strtok incorrectly? is the 's2' pointer messing things up?


I think you are using strtok mostly OK. I'd guess you are getting
messed up by DOS end of line vs unix here. Perhaps depends
on how the configuration file is read (binary vs text?).

-David

 
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Ben Pfaff
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      11-29-2005
Fernando Barsoba <(E-Mail Removed)> writes:

> I'm using strtok() in the following way:


I don't generally recommend using strtok(). It has at least
these problems:

* It merges adjacent delimiters. If you use a comma as
your delimiter, then "a,,b,c" is three tokens, not
four. This is often the wrong thing to do. In fact,
it is only the right thing to do, in my experience,
when the delimiter set is limited to white space.

* The identity of the delimiter is lost, because it is
changed to a null terminator.

* It modifies the string that it tokenizes. This is bad
because it forces you to make a copy of the string if
you want to use it later. It also means that you can't
tokenize a string literal with it; this is not
necessarily something you'd want to do all the time but
it is surprising.

* It can only be used once at a time. If a sequence of
strtok() calls is ongoing and another one is started,
the state of the first one is lost. This isn't a
problem for small programs but it is easy to lose track
of such things in hierarchies of nested functions in
large programs. In other words, strtok() breaks
encapsulation.

--
"You call this a *C* question? What the hell are you smoking?" --Kaz
 
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Fernando Barsoba
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Posts: n/a
 
      11-29-2005
Jack Klein wrote:
> On Tue, 29 Nov 2005 15:16:17 GMT, Fernando Barsoba
> <(E-Mail Removed)> wrote in comp.lang.c:
>
>> Hi,
>>
>> I'm using strtok() in the following way:
>>
>> void obtain_param(char *pmsg, CONF_PARAMS *cnf ) {
>> char *s1, *s2;
>> size_t msg_len;
>>
>> s1 = strtok (pmsg,":");

(...)
> Where did the text string passed in 'pmsg' come from? Was it read
> from a file? If it was read from a file, was the file opened in text
> or binary mode? If you are reading a text file opened in binary mode
> under Windows, you are getting the string as it appears in the file,
> which would be:
>
> "message:this is a test\r\n"
>

Thanks to all for your comments. Indeed, the string I'm getting is
"message:this is a test\r\n". And 'pmsg' comes also from a file. Oddly
enough, I thought I opened the file in text mode. Here's the sequence of
calls:

fp = open_file(argv[1], "r");
cnf = get_param(fp);

-------------
CONF_PARAMS *get_param(FILE *f_param) {
....
p_msg = fgets(param, PARAM_LENGTH, f_param);
....
}
--------
FILE * open_file(char *file_name, char *foptions) {
FILE *fp;
if ((fp = fopen(file_name, foptions)) == NULL) {
printf("Can't open %s\n", file_name);
exit(1);
}
return fp;
}

As the comments pointed out, this seems to be a Windows issue. That's
why in Linux works fine. I'm not opening the file in binary mode though..

F~
 
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Flash Gordon
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Posts: n/a
 
      11-29-2005
Jack Klein wrote:
> On Tue, 29 Nov 2005 15:16:17 GMT, Fernando Barsoba
> <(E-Mail Removed)> wrote in comp.lang.c:


<snip>

>> >>message:this is a test

>>
>> (when 'this is a test\n' is only 14 characters long, w/o the '\n')
>>
>> In other installations (Linux) works just fine, but in my
>> Eclipse/CDT/cygwin sometimes is not.
>>
>> Am I using strtok incorrectly? is the 's2' pointer messing things up?
>>
>> Thanks,
>>
>> F~

>
> Where did the text string passed in 'pmsg' come from? Was it read
> from a file? If it was read from a file, was the file opened in text
> or binary mode? If you are reading a text file opened in binary mode
> under Windows, you are getting the string as it appears in the file,
> which would be:
>
> "message:this is a test\r\n"


Note that since Cygwin is emulating some of Unix it may think of \n as
being the line terminator rather than \r\n even when you open a stream
in text mode, so you could still get a spurious \r. For the intricacies
of Cygwin line termination you will have to ask on a Cygwin mailing
list, but if this is your problem one option is to check if the last
character of the line you read is \r and if so strip it.
--
Flash Gordon
Living in interesting times.
Although my email address says spam, it is real and I read it.
 
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Flash Gordon
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      11-29-2005
Fernando Barsoba wrote:
> Jack Klein wrote:
>> On Tue, 29 Nov 2005 15:16:17 GMT, Fernando Barsoba
>> <(E-Mail Removed)> wrote in comp.lang.c:


<snip>

>> "message:this is a test\r\n"
>>

> Thanks to all for your comments. Indeed, the string I'm getting is
> "message:this is a test\r\n". And 'pmsg' comes also from a file. Oddly
> enough, I thought I opened the file in text mode. Here's the sequence of
> calls:
>
> fp = open_file(argv[1], "r");


Yes, that is opening in text mode.

<snip>

> As the comments pointed out, this seems to be a Windows issue. That's
> why in Linux works fine. I'm not opening the file in binary mode though..


See my previous post, it's a Cygwin issue. Specifically, Cygwin is
emulation Unix to a degree (that is its purpose) so by default it used
the Unix text file conventions. Ask on a Cygwin mailing list for the
details.
--
Flash Gordon
Living in interesting times.
Although my email address says spam, it is real and I read it.
 
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